Oscillator Feedback Circuit for High-Offset Phase Noise Reduction
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Solution Overview
Problem
Existing RF oscillator designs based on Leeson's Rule do not provide negative feedback at high offset frequencies, leading to a higher phase noise floor and increased phase noise at these frequencies, as they assume output impedance does not impact the amplifier's phase noise.
Innovation Solution
The implementation of an oscillator circuit that produces negative feedback at high offset frequencies by leveraging resonators with different reflections at the center frequency and high offset frequencies, using couplers and amplifiers to cancel input signal components and reduce phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If positive amplitude feedback is used to maintain oscillation at the carrier frequency, then oscillation stability is improved, but phase noise at high offset frequencies increases
Solution Approach 1:
The patent applies feedback by introducing a feedback network that samples the oscillator output and feeds it back to the amplifier input. The feedback network includes a resonator configured to provide frequency-dependent feedback: at the carrier frequency, the feedback is positive (0° phase shift) to maintain stable oscillation; at high offset frequencies, the feedback becomes negative (180° phase shift) to reduce phase noise. This dual-mode feedback operation resolves the contradiction between maintaining oscillation stability and reducing high-offset phase noise.
2Device complexity
If no feedback is provided at high offset frequencies, then device complexity is reduced, but phase noise floor increases
Solution Approach 1:
The patent changes the feedback parameter (phase shift) based on frequency. The feedback network is designed so that the phase shift transitions from 0° at the carrier frequency to 180° at high offset frequencies. This parameter change is achieved through the resonator's frequency-dependent impedance characteristics and the feedback network configuration. By dynamically changing the feedback parameter according to frequency, the system reduces phase noise floor without requiring completely separate feedback circuits for different frequency regions.
3Object-generated harmful factors
If resonator reflection is used to provide feedback, then phase noise reduction is achieved, but gain at resonant frequency is reduced
Solution Approach 1:
The patent applies local quality by making the feedback characteristics frequency-specific. The feedback network is designed so that only signals at high offset frequencies receive strong negative feedback through the resonator reflection, while signals at the resonant frequency experience minimal feedback effect. This is achieved by configuring the resonator and feedback network such that the reflection coefficient is high at offset frequencies but low at the resonant frequency, thereby locally targeting the feedback action to where it is most needed without compromising overall gain.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces phase noise and the phase noise floor at high offset frequencies, improving oscillator performance compared to traditional designs that do not provide feedback in these regions.
Implementation Method 1
resonators with different reflections at the center frequency and high offset frequencies
Implementation Method 2
leveraging resonators with different reflections at the center frequency and high offset frequencies
Data Source
AI summary
An oscillator includes a resonator and a first loop circuit. The first loop circuit includes an amplifier and a first coupler. That first loop circuit is electrically coupled to the resonator. The oscillator is configured to produce negative feedback for the amplifier in a cavity mode relative to short circuit terminations or open circuit terminations of a cavity modelling the oscillator at frequencies offset from a carrier frequency. The oscillator has a loss of less than 4.00 dB for a bidirectional trip through the cavity at the frequencies offset from the carrier frequency.